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Superconductivity was the field of study where the idea for the Higgs originated in the 1960s. But the particle proved impossible to witness because it decays so fast. This new signature was glimpsed as very thin, chilled layers of metal compounds were pushed very close to the boundary of their superconducting state. This process creates a “mode” in the material that is analogous to the Higgs Boson but lasts much longer.

Rather than the study of particles, it belongs in the field known condensed matter physics; it also uses much less energy than experiments at the LHC, where protons are smashed together at just under the speed of light. It was at the LHC in 2012 that the Higgs Boson, believed to give all the other subatomic particles their mass, was detected for the very first time.

The new superconductor discovery was presented amid much discussion at this week’s March Meeting of the American Physical Society in San Antonio, Texas. It also appeared in the journal Nature Physics in January. Speaking at the meeting, Prof Aviad Frydman from Bar Ilan University in Israel responded in no uncertain terms to the suggestion that his work could substitute for the LHC. “That’s complete nonsense,” he told the BBC. “In fact it’s kind of embarrassing.”

The team used superconducting films made from compounds of niobium (pictured here as a fibre) and indium

Prof Frydman said the convergence of results from “two extremes of physics” was the most striking aspect of his findings, which were the fruit of a collaboration spanning Israel, Germany, Russia, India and the USA. “You take the high energy physics, which works in gigaelectronvolts. And then you take superconductivity, which is low energy, low temperature, one millivolt. “You have 10 to the 15 (one quadrillion) orders of magnitude between them, and the same physics governs both! That is the nice thing.”

“It’s not that our experiment can replace the LHC. It’s completely separate.”

Superconductors are materials that, when under critical conditions including temperatures near absolute zero (-273C), allow electrons to move with complete freedom. It was attempts to understand this property that ultimately led to Peter Higgs and others proposing the now-famous boson. “In the 1960s there were two distinct, basic problems. One was superconductivity and one was the mass of particles,” Prof Frydman explained.

“People like Phil Anderson developed this mechanism for understanding superconductivity. And the guys from high energy saw this kind of solution, and applied it to high energy physics. That’s where the Higgs actually came from.” So the detection of a superconducting Higgs, he added, is “closing a historical circuit”. This closure was a long time coming. Detecting the Higgs in a superconductor had seemed almost impossible. This was because the energy required to excite (and detect) the Higgs mode – even though vastly less than that needed to generate its analogous particle inside the LHC – would destroy the very property of superconductivity. The Higgs mode would vanish almost before it arose. But when Prof Frydman and his colleagues held their thin films in conditions very close to the “critical transition” between being a superconductor and an insulator, they created a longer-lived, lower-energy Higgs mode.

Other claims of a superconducting Higgs have been made in the past, including one in 2014. They have all faced criticism. Indeed, Prof Frydman’s conference presentation was also greeted with intense questions from others in the field. “Like any physical finding, there are different interpretations,” he said. “The Cern experiment is also being contested.”

On a fall morning in 2009, a team of three young physicists huddled around a computer screen in a small office overlooking Broadway in New York. They were dressed for success—even the graduate student’s shirt had buttons—and a bottle of champagne was at the ready. With a click of the mouse, they hoped to unmask a fundamental particle that had eluded physicists for decades: the Higgs boson.

Of course, these men weren’t the only physicists in pursuit of the Higgs boson. In Geneva, a team of hundreds of physicists with an $8 billion machine called the Large Hadron Collider, and the world’s attention, also was in the hunt. But shortly after starting for the first time, the LHC had malfunctioned and was offline for repairs, opening a window three guys at NYU hoped to take advantage of.

The key to their strategy was a particle collider that had been dismantled in 2001 to make room for the more powerful LHC. For $10,000 in computer time, they would attempt to show that the Large Electron-Positron collider had been making dozens of Higgs bosons without anybody noticing.

“Two possible worlds stood before us then,” said physicist Kyle Cranmer, the leader of the NYU group. “In one, we discover the Higgs and a physics fairy tale comes true. Maybe the three of us share a Nobel prize. In the other, the Higgs is still hiding, and instead of beating the LHC, we have to go back to working on the LHC.”

Cranmer had spent years working on both colliders, beginning as a graduate student at the Large Electron-Positron collider. He had been part of a 100-person statistical team that combed through terabytes of LEP data for evidence of new particles. “Everyone thought we had been very thorough,” he said. “But our worldview was colored by the ideas that were popular at the time.” A few years later, he realized the old data might look very different through the lens of a new theory.

So, like detectives poring through evidence in a cold case, the researchers aimed to prove that the Higgs, and some supersymmetric partners in crime, had been at the scene in disguise.

Dreaming up the Higgs

The Higgs boson is now viewed as an essential component of the Standard Model of physics, a theory that describes all known particles and their interactions. But back in the 1960s, before the Standard Model had coalesced, the Higgs was part of a theoretical fix for a radioactive problem.

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

Here’s the predicament they faced. Sometimes an atom of one element will suddenly transform into an atom of a different element in a process called radioactive decay. For example, an atom of carbon can decay into an atom of nitrogen by emitting two light subatomic particles. (The carbon dating of fossils is a clever use of this ubiquitous process.) Physicists trying to describe the decay using equations ran into trouble—the math predicted that a sufficiently hot atom would decay infinitely quickly, which isn’t physically possible.

To fix this, they introduced a theoretical intermediate step into the decay process, involving a never-before-seen particle that blinks into existence for just a trillionth of a trillionth of a second. As if that weren’t far-fetched enough, in order for the math to work, the particle—called the W boson—would need to weigh 10 times as much as the carbon atom that kicked off the process.
“Figuring out what happened in a collider is like trying to figure out what your dog ate at the park yesterday. You can find out, but you have to sort through a lot of shit to do it.”

To explain the bizarrely large mass of the W boson, three teams of physicists independently came up with the same idea: a new physical field. Just as your legs feel sluggish and heavy when you wade through deep water, the W boson seems heavy because it travels through what became known as the Higgs field (named after physicist Peter Higgs, who was a member of one of the three teams). The waves kicked up by the motion of this field, by way of a principle known as wave-particle duality, become particles called Higgs bosons.

Their solution boiled down to this: Radioactive decay requires a heavy W boson, and a heavy W boson requires the Higgs field, and disturbances in the Higgs field produce Higgs bosons. “Explaining” radioactive decay in terms of one undetected field and two undiscovered particles may seem ridiculous. But physicists are conspiracy theorists with a very good track record.

Forensic physics

How do you find out if a theoretical particle is real? By the time Cranmer came of age, there was an established procedure. To produce evidence of new particles, you smash old ones together really, really hard. This works because E = mc2 means energy can be exchanged for matter; in other words, energy is the fungible currency of the subatomic world. Concentrate enough energy in one place and even the most exotic, heavy particles can be made to appear. But, they explode almost immediately. The only way to figure out they were there is to catch and analyze the detritus.

How particle detectors work

The innermost layer of a modern detector is made of thin silicon strips, like in a camera. A zooming particle, such as an electron, leaves a track of activated pixels. The track curves slightly, thanks to a magnetic field, and the degree of curvature reveals the electron’s momentum. Next the electron enters a series of chambers of excitable gas, where it ionizes little trails behind it. An electric field pulls the charged trails over to an array of wire sensors. Finally, the electron enters an iron or steel calorimeter which slows the particle to a halt, gathering and recording all of it’s energy.

Modern particle accelerators like the LEP and LHC are like high-tech surveillance states. Thousands of electronic sensors, photoreceptors, and gas chambers monitor the collision site. Particle physics has become a forensic science.

It’s also a messy science. “Figuring out what happened in a collider is like trying to figure out what your dog ate at the park yesterday,” said Jesse Thaler, the MIT physicist who first told me of Cranmer’s quest. “You can find out, but you have to sort through a lot of shit to do it.”

The situation may be even worse than that. To reason backward from the particles that live long enough to detect to the short-lived undetected ones, requires detailed knowledge of each intermediate decay—almost like an exact description of all the chemical reactions in the dog’s gut. Complicating matters further, small changes in the theory you’re working with can affect the whole chain of reasoning, causing big changes in what you conclude really happened.
The fine-tuning problem

While the LEP was running, the Standard Model was the theory used to interpret its data. A panoply of particles were made, from the beauty quark to the W boson, but Cranmer and others had found no sign of a Higgs. They started to get worried: If the Higgs wasn’t real, how much of the rest of the Standard Model was also a convenient fiction?

The model had at least one troubling feature beyond a missing Higgs: For matter to be capable of forming planets and stars, for the fundamental forces to be strong enough to hold things together but weak enough to avoid total collapse, an absurdly lucky cancellation (where two equivalent units of opposite sign combine to make zero) had to occur in some foundational formulas. This degree of what’s known as “fine-tuning” has a snowball’s chance in hell of happening by coincidence, according to physicist Flip Tanedo of the University of California, Irvine. It’s like a snowball never melting because every molecule of scorching hot air whizzing through hell just happens to avoid it by chance.

So Cranmer was quite excited when he got wind of a new model that could explain both the fine-tuning problem and the hiding Higgs. The Nearly-Minimal Supersymmetric Standard Model has a host of new fundamental particles. The cancellation which seemed so lucky before is explained in this model by new terms corresponding to some of the new particles. Other new particles would interact with the Higgs, giving it a covert way to decay that would have gone unnoticed at the LEP.

Standard Model of Supersymmetry

If this new theory was correct, evidence for the Higgs boson was likely just sitting there in the old LEP data. And Cranmer had just the right tools to find it: He had experience with the old collider, and he had two ambitious apprentices. So he sent his graduate student James Beacham to retrieve the data from magnetic tapes sitting in a warehouse outside Geneva, and tasked NYU postdoctoral researcher Itay Yavin with working out the details of the new model. After laboriously deciphering dusty FORTRAN code from the original experiment and loading and cleaning information from the tapes, they brought the data back to life.

This is what the team hoped to see evidence of in the LEP data:

First, an electron and positron smash into each other, and their energy converts into the matter of a Higgs boson. The Higgs then decays into two ‘a’ particles—predicted by supersymmetry but never before seen—which fly in opposite directions. After a fraction of a second, each of the two ‘a’ particles decays into two tau particles. Finally each of the four tau particles decays into lighter particles, like electrons and pions, which survive long enough to strike the detector.

As light particles hurtled through the detector’s many layers, detailed information on their trajectory was gathered (see sidebar). A tau particle would appear in the data as a common origin for a few of those trails. Like a firework shot into the sky, a tau particle can be identified by the brilliant arcs traced by its shrapnel. A Higgs, in turn, would appear as a constellation of light particles indicating the simultaneous explosion of four taus.

Unfortunately, there are almost guaranteed to be false positives. For example, if an electron and a positron collide glancingly, they could create a quark with some of their energy. The quark could explode into pions, mimicking the behavior of a tau that came from a Higgs.

A computer simulation of a Higgs decaying into more elementary particles. The colored tracks show what the detector would see. ALEPH Collaboration/CERN

To claim that a genuine Higgs had been made, rather than a few impostors, Beacham and Yavin needed to be extremely careful. Electronics sensitive enough to measure a single particle will often misfire, so there are countless decisions about which events to count and which to discard as noise. Confirmation bias makes it too dangerous to set those thresholds while looking at actual data from the LEP, as Beachem and Yavin would have been tempted to shade things in favor of a Higgs discovery. Instead, they decided to build two simulations of the LEP. In one, collisions took place in a universe governed by the Standard Model; in the other, the universe followed the rules of the Nearly-Minimal Supersymmetric Model. After carefully tuning their code on the simulated data, the team concluded that they had enough power to proceed: If the Higgs had been made by the LEP, they would detect significantly more four-tau events than if it had not.
Moment of theoretical truth

The team was hopeful and nervous as the moment of truth approached. Yavin had hardly been sleeping, checking and re-checking the code. A bottle of champagne was ready. With one click, the count of four-tau events at the LEP would come onscreen. If the Standard Model was correct, there would be around six, an expected number of false positives. If the Nearly-Minimal Supersymmetric Standard Model was correct, there would be around 30, a big enough excess to conclude that there really had been a Higgs.

“Honey, we didn’t find the Higgs,” Cranmer told his wife on the phone. Yavin collapsed in his chair. Beacham was thrilled the code had worked at all, and drank the champagne anyway.

If Cranmer’s little team had found the Higgs boson before the multi-billion-dollar LHC and unseated the Standard Model, if the count had been 32 instead of 2, their story would have been front-page news. Instead, it was a typical success for the scientific method: A theory was carefully developed, rigorously tested, and found to be false.

“With one keystroke, we rendered over a hundred theory papers null and void,” Beacham said.

Three years later, a huge team of physicists at the LHC announced they had found the Higgs and that it was entirely consistent with the Standard Model. This was certainly a victory—for massive engineering projects, for international collaborations, for the theorists who dreamt up the Higgs field and boson 50 years ago. But the Standard Model probably won’t stand forever. It still has problems with fine-tuning and with integrating general relativity, problems that many physicists hope some new model will resolve. The question is, which one?

“There are a lot of possibilities for how nature works,” said physicist Matt Strassler, a visiting scholar at Harvard University. “Once you go beyond the Standard Model, there are a gazillion ways to try to fix the fine-tuning problem.” Each proposed model has to be tested against nature, and each test invariably requires months or years of labor to do right, even if you’re cleverly reusing old data. The adrenaline builds until the moment of truth—will this be the new law of physics? But the vast number of possible models means that almost every test ends with the same answer: No. Try again.

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Friday, July 25, 2014
Jim Pivarski

Nearly 50 years before its discovery, the Higgs field was proposed as a way to explain why particles have mass. The Standard Model would be internally inconsistent if particles could have mass on their own (that is, as an intrinsic property like charge), but it would not be inconsistent to propose a new field that gives them an effective mass by interacting with them. That new field has come to be known as the Higgs field, and particles of this field are called Higgs bosons.

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

Higgs Field simulation

This story is well known, and it was told in many ways when the Higgs boson was discovered in 2012. What is less well known is that the problem of mass was not a single problem. The reason that force particles (such as W and Z bosons) cannot have intrinsic mass is different from the reason that matter particles (such as electrons and quarks) cannot have intrinsic mass. The effective mass of force particles and matter particles could come from different sources. There could be two Higgs fields, one that only interacts with and gives mass to force particles, the other to matter particles, or perhaps the mechanisms themselves could be completely different.

Many physicists expected that a single Higgs field would pull double duty and give mass to all the particles. This, however, was a hypothesis, based on the expectation that nature is simple and elegant.

As it turns out, nature seems to be simple and elegant. CMS scientists recently published a study of Higgs boson decays to matter particles, complementing its discovery, which was through its decays to force particles. The same Higgs field interacts with both types of particles in the expected way.

Specifically, the study focused on Higgs to tau pairs (tau is a heavy cousin of the electron) and Higgs to b quarks (the b quark is a heavy cousin of the quarks found in the protons and neutrons of an atom). Since this interaction is responsible for mass, it is stronger for more massive particles. Both of these decay products are hard to distinguish from backgrounds, especially the b quarks, so the statistical significance is weak (3.8 sigma, equivalent to a one in 14,000 chance that the combined observation is spurious). However, these decays and all the decays to force particles point back to a single Higgs boson. The basic principles of physics may yet be simple enough to fit on the front of a T-shirt.

The quark structure of the proton. (The color assignment of individual quarks is not important, only that all three colors are present.)

The quark structure of the neutron. (The color assignment of individual quarks is not important, only that all three colors are present.)

Cameras were rolling in CERN’s building 40 on Tuesday when members of the ATLAS and CMS collaborations heard the news from the Swedish Academy of Sciences that François Englert and Peter W. Higgs had received the 2013 Nobel prize in physics. Watch their reaction in the video above.

The Nobel prize was awarded to Englert and Higgs “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider.” The ATLAS and CMS collaborations announced their discovery of the particle at CERN on 4 July 2012.

As the news came through from Stockholm, CERN physicists burst into applause, and CERN Director-General Rolf Heuer gave a spontaneous speech congratulating the theoretical physicists for the award and the experimental physicists at CERN for their discovery.

The ATLAS and CMS collaborations each involves more than 3000 people from all around the world. They have constructed sophisticated instruments – particle detectors – to study proton collisions at CERN’s Large Hadron Collider (LHC), itself a highly complex instrument involving many people and institutes in its construction.

The Royal Swedish Academy of Sciences awarded the Nobel Prize in physics today to theorists Peter Higgs and Francois Englert to recognize their work developing the theory of what is now known as the Higgs field, which gives elementary particles mass.

U.S. scientists, including researchers at Lawrence Livermore National Laboratory (LLNL), played a significant role in advancing the theory and in discovering the particle that proves the existence of the Higgs field, the Higgs boson.

Nearly 2,000 physicists from U.S. institutions — including 89 U.S. universities and seven U.S. Department of Energy laboratories — participate in the ATLAS and CMS experiments, making up about 23 percent of the ATLAS collaboration and 33 percent of CMS at the time of the Higgs discovery. Brookhaven National Laboratory serves as the U.S. hub for the ATLAS experiment, and Fermi National Accelerator Laboratory serves as the U.S. hub for the CMS experiment. U.S. scientists provided a significant portion of the intellectual leadership on Higgs analysis teams for both experiments.

Lawrence Livermore joined the Compact Muon Solenoid (CMS) experiment in 2005. LLNL contributions include: assisted in development of the trigger system that captures Higgs and other phenomena for the CMS experiment; and a leadership role in developing the software that reconstructs raw data into the physics objects that form the basis of all analyses. Lab researchers are now working on a novel physics analysis and leading a detector upgrade that can discover new particles and reveal information about the Higgs.

Lowering of the final element (YE-1) of the Compact Muon Solenoid (CMS) detector into its underground experimental cavern.

The LLNL team on CMS is Doug Wright, David Lange, Jeff Gronberg and postdoc Finn Rebassoo. Former LLNL postdocs currently on CMS are Jonathan Hollar (now at University of Louvain, Belgium) and Bryan Dahmes (now at University of Minnesota).

CERN Director-General Rolf Heuer accepts an Edinburgh Medal on behalf of CERN at a ceremony on Saturday. Also honoured was Peter Higgs (right) (Image: Joshua Smythe)

“In a ceremony on 24 March, the 2013 Edinburgh Medal was awarded to Peter Higgs and CERN. The Director-General received the medal on behalf of CERN [See video].

The Edinburgh Medal, now in its 25th year, is awarded by the Edinburgh International Science Festival to scientists whose achievements have made a significant contribution to the understanding and well-being of humanity.

The first Edinburgh Medal was awarded to Abdus Salam who received the Nobel prize in physics for theoretical work that became a fundamental part of the Standard Model of particles and forces. Salam’s work incorporated what is now known as the Brout-Englert-Higgs mechanism, which gives mass to elementary particles. The mechanism introduced a new field, which like all fundamental fields has an associated particle, in this case called the Higgs boson.

This year the award comes full circle, being awarded to Higgs and to CERN, where the ATLAS and CMS experiments at the Large Hadron Collider tracked down a particle last summer that look increasingly like a Higgs boson.

“Physicists speaking today at the Moriond conference in La Thuile, Italy, have announced that the new particle discovered at CERN last year is looking more and more like a Higgs boson. However, more analysis is still required before a definitive statement can be made. The key to a positive identification of the particle is a detailed analysis of its properties and the way that it interacts with other particles. Since the announcement last July, much more data has been analysed, and these properties are becoming clearer.

The key property that will allow us to say whether or not it is a Higgs particle is called spin. If this particle has spin-zero, then it is a Higgs particle. If not, then it is something different, possibly linked to the way gravity works. All the analysis conducted so far strongly indicates spin-zero, but is not yet able to rule out entirely the possibility that the particle has spin-two.

‘Until we can confidently tie down the particle’s spin,’ said CERN Research Director Sergio Bertolucci, ‘the particle will remain Higgs-like. Only when we know that is has spin-zero will we be able to call it a Higgs.’

Even then, the work will be far from over. If the new particle is a Higgs, it could be the Higgs as predicted in the 1960s, which would complete the Standard Model of particle physics, or it could be a more exotic particle that would lead us beyond the Standard Model. The stakes are high. The Standard Model accounts for all the visible matter in the Universe, including the stuff that we are made of, but it does not account for the 96% of the Universe that is invisible to us – the dark universe. Finding out what kind of Higgs it is will rely on carefully measuring the particle’s interactions with other particles, and that may take several years to resolve.

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Friday, Jan. 11, 2013
Don Lincoln

“On July 4, 2012, the CMS and ATLAS experiments announced the discovery of a new particle with a mass of 125 GeV. This particle was widely heralded in the press as the Higgs boson, but both experiments very carefully didn’t make that claim. Instead, both experiments used the language “a particle consistent with being a Higgs boson.”

One possible signature of a Higgs boson from a simulated collision between two protons. It decays almost immediately into two jets of hadrons and two electrons, visible as lines. (Wikipedia)

So why were the experiments so cagey in their announcement?

So what do we know? Well, evidence suggested that the discovered boson decayed into pairs of fermions (bottom quarks and tau leptons, both with spin 1/2) and pairs of bosons (W and Z bosons and photons, with spin 1). From this simple observation, we can infer that the newly discovered particle was electrically neutral (a prediction of Higgs theory) and was a boson (another successful prediction). In addition, using what we know about the spin of the decay products and combining that with the rules of quantum mechanics, we also know from the particle’s decay into bosons that the spin of the parent had to be 0 or 2.

A spin 0 particle would support the Higgs hypothesis, while a spin 2 particle, not being predicted, might be even more interesting. On the other hand, the universe might be malicious, and the July 2012 announcement could be referring to not only one, but maybe two particles, with spins of 0 or 2 and with masses close enough to each other that we thought we were seeing just one particle when we might actually have been seeing two….”

Now it is getting really deep and intense, so see Don’s full article here.